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Aug." 28'; ' 1962
E. M. GYORGY ETAL
3,051,917
METHOD OF SUPPRESSING SATURATION EFFECTS IN GYROMAGNETIC DEVICES
Filed June 22, 1960
2 Sheets-Sheet 1
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3,051,917
E. M. GYORGY ETAL
METHOD OF SUPPRESSING SATURATION EFFECTS IN GYROMAGNETIC DEVICES
Filed June 22, 1960
2 Sheets-Sheet 2
.
E. M GVORGV
WVENTZRS'H.
E. 0. sea V/L
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$51,917
United States
Patented Aug. 28, 1962
2
1
1957.
3,051,917
At high power levels the coupling of energy
from the uniform precession to the spin waves is en
METHOD OF SUPPRESSING SATURATIGN
hanced, substantially modifying the transmission prop
EFFECTS IN GYROMAGNETIC DEVICES
erties of the gyromagnetic material.
‘It is, accordingly, a more speci?c object of this inven
Ernst M. Gyorgy, Morris Plains, and Henry E. D. Scovil,
New Vernon, N.J., assignors to Bell Telephone Labora
tories, Incorporated, New York, N.Y., a corporation of
New York
tion to inhibit the transfer of power between the uni
form precession and the short wavelength spin waves.
Investigation has shown that the spin waves propagate
within the gyromagnetic material in a preferred direc
tion with respect to the uniform precession, and have a
?nite build-up time. In accordance with the invention,
This invention relates to electromagnetic wave devices
means are provided whereby the direction of the uniform
using gyromagnetic materials and, in particular, to means
precession is changed at intervals comparable to or less
for eliminating the anomalous attenuation etfects pro
than the build-up time of the spin waves. By so modulat
duced by such gyromagnetic materials at high power
15 ing the sense of the uniform precession there is insuf?cient
levels.
coupling between the uniform precession and the spin
It has been observed that materials of the type having
waves to enable their growth and propagation within the
the properties described by the mathematical analysis
Filed June 22, 196i}, Ser. No. 38,938
8 Claims. (Cl. 33>3—3l)
of D. Polder, Philosophical Magazine, volume 40, pages
99 through 115 (1949'), have certain anomalous attenua
tion characteristics which were not predicted by Polder’s
theory. This class of materials, a chief one ‘among them
being ferrite, is characterized by certain unpaired electron
spins which respond to a transmitted microwave signal
by precessing gyroscopically about the line of an applied
magnetic ?eld. The interaction of these precession elec
gyromagnetic material. The suppression of the above
mentioned short wavelength spin waves effectively avoids
the so-called anomalous large-signal behavior of gyro
magnetic materials.
The above-stated and other objects and advantages, the
nature of the present invention, and its various fea
tures, ‘will appear more fully upon consideration of the
25 various illustrative embodiments now to be described in
trons with the applied microwave signal results in cer
detail in connection with the accompanying drawings, in
tain magnetic properties which have given these materials
which:
FIG. 1, given for the purpose of explanation, is a
the name “gyromagnetic.” Polder’s so-called “small
graphical and qualitative representation of the attenua
signal” theory predicts an attenuation characteristic as
shown by the solid curve ~10 in FIG. 1 of the drawings. 30 tion versus applied magnetic ?eld characteristic of gyro
magnetic media showing the small signal and large
Also shown in FIG. 1 is dashed curve 11 representing what
signal responses;
may be called the large signal response of gyromagnetic
FIGS. 2a and 2b, given for the purpose of explanation,
materials. It will be observed that the large signal re
are graphical and qualitative representations of the at
sponse exhibits certain anomalous characteristics in the
regions .of two particular applied ?eld values which are 35 tenuation versus applied power characteristics of gyro
magnetic media at the ?eld values HS and Hm, respec
not predicted by Polder’s theory and are not present at
tively, shown in FIG. 1;
smaller signal levels. Thus, at the ?eld value HS, the at
FIG. 3 is a perspective view of an illustrative embodi
tenuation for large signals is much greater than for
ment of the invention in which the modulating ?eld is
small signal-s, while at another ?eld value Hm, the attenua
applied in the direction opposite to the magnetizing ?eld;
tion for large signals is much less than that for small
FIG. 4, given by way of explanation, is a graph show
signals. This large signal behavior of gyromagnetic ma
ing the hysteresis loop of a typical sample of gyromag
terials has been observed by R. W. Damon, Review of
netic material;
Modern Physics, volume 25, pages 239 through 245, Jan
‘FIG. 5 is a perspective view of a second embodiment
uary 1953, and by N. Bloembergen and S. Wang, Physi 45
of the invention in which the modulating ?eld is applied
cal5 Review, volume 93, pages 72 through 83, January
oblique to the biasing ?eld;
19 4.
FIG. 6 shows a third embodiment of the invention il
The effect of this large signal behavior has been to
lustrative of a method of reducing instantaneous varia
severely limit the operating range of electromagnetic
tions in the transmission properties of microwave devices
wave devices employing gyromagnetic materials.
produced by the modulating ?eld; and
Gyromagnetic devices can be broadly divided into two
‘FIG. 7, given by way of explanation, shows the man
classes: those biased below gyromagnetic resonance and
ner in which the instantaneous phase shift of the device
which depend for their operation upon the effective
shown in FIG. 6 varies under the in?uence of the modu
permeability of the gyromagnetic element and its low
attenuation, and those biased at resonance and which de 55 lating ?eld.
Referring more particularly to FIG. 1, there is shown,
pend upon the effective high attenuation of the gyromag
for the purpose of explanation, a graphical and qualita
netic element.
tive representation of the attenuation (a) as a function of
Because the so-called “large signal” effects can, in fact,
the applied magnetic biasing ?eld characteristic of gyro
occur at relatively low power levels, the performance
of both classes of devices over a substantial range of op 60 magnetic materials. The term “gyromagnetic material”
is employed here in its accepted sense as designating the
erating signal levels is adversely effected by the anomalous
class of magnetic polarizable materials having unpaired
characteristics of gyrornagnetic materials.
spin systems involving portions of the atoms thereof that
It is, therefore, an object of this invention to avoid the
are capable of being aligned by an external magnetic
so-called “large signal” behavior of gyromagnetic ma
polarizing ?eld and which exhibit a signi?cant preces
terials.
65 sional motion at a frequency within the range contem~
The anomalous behavior of gyromagnetic materials at
plated by the invention under the combined in?uence of
high power levels has been explained as due to the excita
said polarizing ?eld and a varying magnetic ?eld com
ponent. This precessional motion is characterized as
entitled “The Theory of Ferromagnetic Resonance at 70 having an angular momentum and a magnetic moment.
Typical of such materials are the ferromagnetic materials
High Signal Powers,” The Journal of the Physics and
including the spinels such as magnesium aluminum fer
Chemistry of Solids, volume 1, pages 209-227, April
tion within the material of a class of short wavelength
spin waves. (This is discussed by H. Suhl in an article
3,051,917
3
4
rite, aluminum zinc ferrite and the garnet-like materials
the microwave signal has not increased appreciably. So
such as yttrium-iron garnet.
far the conditions have remained within the scope of the
_
Solid curve 10 shows this characteristic for small signal
levels below a critical value, to be discussed more fully
below, and dashed curve 11 shows this characteristic for
large signal levels above the critical value: The behavior
of a gyromagnetic medium for small signals has been
explained on the-theory that in the presence of an ap
plied magnetic ?eld having an amplitude great enough-to
small signal theory.
As the power level of the applied signal continues to
increase, however, a critical point is reached where the
preferred band of spin waves can no longer transfer en
ergy to the remainder of the spin Wave system as fast as
it is being received from the uniform precession. At this
point, called the critical power level, the preferred band
saturate the magnetic material, the unpaired electron spms 10 goes to a higher state of excitation to accommodate the
in the medium line up parallel to one another and tend to
behave gyroscopically as a single unit. Therefore, when
increase in energy level. The excitation of the preferred
band tends to build up rapidly since the coupling thereto
the frequency of the applied signal is equal to the natural
is nonlinear, increasing with increasing signal level. This
precession frequency of the electron spins, a resonant
band, being resonant with the uniform precession, is now
condition exists under which the electron spins are able 15 more strongly coupled to the uniform precession and
to absorb large amounts of energy from the signal. This
therefore receives even more energy from the uniform
condition, which has been called the main gyromagnetic
precession. This further increases the excitation level
resonance, is shown at the applied ?eld value Hm in FIG.
of the preferred band, allowing even further amounts of
1. At all other ?eld values the attenuation is very low
energy to be coupled thereto. This build-up cycle con
and may be neglected.
20 tinues until the power absorbed by the preferred band is
The simple uniform precession theory used above, how
just su?icient to balance the losses of the resonant system.
ever, does not explain the shape of the attenuation charac
teristic at large signal levels, represented by dashed curve
11 in FIG. 1. At these large signal levels, the attenuation
at main resonance becomes substantially lower and the
resonance curve becomes substantially broader than at
small signal levels. Furthermore, a second resonance,
which may be termed the subsidiary resonance, appears at
It can be seen that an unstable condition exists at the
critical power level which results in large amounts of
energy being absorbed from the applied signal. This re
sults in a large increase in the attenuation offered to the
applied signal. Any further increase in the power level
of the applied signal is substantially all diverted into the
an applied ?eld value of HS, substantially less than Hm.
An attempt will be made below to explain this anomalous
preferred spin wave band. This condition is shown as
the subsidiary resonance hump in dashed curve 11 of FIG.
1 at applied ?eld value H5. The change in attenuation
behavior of polarized gyromagnetic media at high sig
can more readily be seen in FIG. 2a.
nal levels.
The small signal theory states that a microwave signal
passing through a polarized gyromagnetic medium is cou
pled to the electron spins within the medium by means of
In FIG. 2a there is shown, for the purpose of explana
tion, a graphical and qualitative representation of the at
the high frequency magnetic ?eld components of the
applied signal.
The electron spins are thus driven en
masse to precess gyroscopically at some angle about the
line of the applied magnetic ?eld. Not taken into ac
count by this small signal theory is the coupling between
this uniform precession of the electron spins and certain
small perturbances in the electron spin system which may
tenuation versus power input characteristic of a gyro
magnetic medium biased to a ?eld value Hs as shown in
FIG. 1. It can be seen that the attenuation is very low
for power inputs below the critical power PM. At this
point, however, the attenuation suddenly jumps to a very
high value due to the resonance between the uniform
precession and the preferred spin wave band. Beyond
this point the attenuation decreases slightly but retains
substantially its high value. The power level at which
be called spin waves.
the run-away condition occurs is a function of the mag
A gyromagnetic medium is continually in a state of
netic state of the gyromagnetic medium and the relaxa
thermal agitation, resulting in a minute and somewhat 45 tion time of the preferred spin Waves.
random misalignment of the electron spins. These per
In the case of the main resonance at an applied mag
turbances can, by means of a Fourier analysis, be resolved
netic ?eld of Hm, the uniform precession is again cou—
into a series of waves, called “spin Waves,” which are all
pled to a preferred band of spin Waves having a fre
coupled to each other and to the uniform precession by
quency and direction of resonance closely resembling that
means of interspin magnetic forces and electrostatic
of the uniform precession. Under this condition, how
forces called exchange ?elds. A relatively narrow band
ever, the uniform precession is already absorbing large
of these spin waves, which may be called the preferred
amounts of energy from the applied signal and is there
band, is much more strongly coupled to the uniform pre
fore near its maximum state of excitation. When the
cession than the remainder of the spin waves due to a
critical power level is reached and the preferred spin
correspondence between their resonances in frequency and 55 wave band can no longer get rid of energy as fast as it
direction. The spin wave system, and especially the pre
receives it, the preferred spin waves go to a higher state
ferred band, can, by means of this coupling, absorb energy
of excitation at the expense of the uniform precession.
from the uniform precession. However, under conditions
The removal of energy from the uniform precession de
within the scope of the small signal theory, the energy loss
creases the coupling of this precession to the applied sig
to the spin wave system is su?iciently small to be negli 60 nal and hence the attenuation olfered to the signal also
gible.
decreases. Further increases in the power level of the
The condition of subsidiary resonance, represented by
HS in FIG. ll, will now be investigated. When biased be
applied signal result in further excitation of the preferred
spin waves and a larger decoupling of the uniform preces
sion from the applied signal. The attenuation therefore
coupled to the uniform precession due to the lack of 65 decreases and eventually goes to zero when the uniform
low resonance, only very small amounts of energy can be
correspondence between the applied frequency and the
precession is completely decoupled from the applied sig
natural resonant frequency of the uniform precession.
nal. This condition is shown as the decline and broaden
However, a small increase in the applied signal will
ing of the main resonance peak in dashed curve 11 of
nevertheless raise the excitation of the uniform precession
FIG. 1 at applied ?eld value Hm. The change in attenua
slightly, allowing small amounts of energy to be trans 70 tion can more readily be seen by considering FIG. 2b.
ferred to the preferred spin wave band and thence to the
In FIG. 2b there is shown, for the purpose of explana
remainder of the spin wave system. Eventually this en
tion, a graphical and qualitative representation of the at
ergy is transmitted to the crystal lattice to be dissipated as
tenuation versus power input characteristic of a gyro
heat. Since the excitation level of the spin wave system
magnetic medium biased by a ?eld Hm as shown in FIG. 1.
has not changed appreciably, the attenuation offered to 75 It can be seen that the attenuation is very high for
3,051,917
power inputs below the critical power P02. At this point,
however, the attenuation suddenly drops to a low value.
6
past vane 31 with substantially little or no ‘attenuation.
Under this condition source 36 is gated off. As the power
level of the propagating wave increases and approaches
Thereafter, the attenuation continues to decrease, ap
the critical power level, source 36 is gated on. The out
proaching zero. The critical power level at which the de
put of source 36 is a wave having an amplitude and fre
cline in attenuation begins has been found to be governed
quency to reverse the direction of magnetization at a
by the same factors as govern the critical power level at
rate related to the spin wave build-up time in vane 31.
subsidiary resonance.
To determine the amplitude of the modulating ?eld
In FIG. 3 a reciprocal phase shifter is shown, modi?ed
necessary
to reverse the magnetization when the magnetic
in accordance with the invention to eliminate subsidiary
resonance effects and to thereby produce low-loss phase 10 material is biased at or above saturation, reference is
made to ‘FIG. 4 which shows a typical hysteresis loop
shift at radio frequency power levels substantially greater
for the gyromagnetic material. Speci?cally, FIG. 4
than the critical power level for the gyromagnetic ma
shows the relationship between the magnetomotive force
or magnetizing ?eld H and the magnetic ?ux density B.
wave energy, which may be a rectangular waveguide of 15 Assuming the biasing magnetization to be -—Hd.c, the
magnetic state of the material is that given by point
the metallic shield type having a .wide internal cross-sec
(1) on FIG. 4. To reduce the magnetic ?ux, B, to zero
tional dimension of at least one-half wavelength of the
from point (1) would require a reverse magnetomotive
wave energy to be conducted thereby and ‘a narrow di
force of Hc-l-Hdc, where Hc is the coercive force for
mension substantially one-half of the wide dimension.
Included within guide 30‘ are means for imparting a 20 the material. This is indicated at point (2). To
now reverse the magnetic ?ux in the magnetic material
phase delay to the wave energy propagating therethrough.
terial. Speci?cally, the phase shifter comprises a guide
30 of ‘bounded electrical transmission line for guiding
In particular, disposed within guide 30 is a thin vane 31
of gyromagnetic material. Vane 31 is symmetrically dis
to some point (3), the application of an additional mag
netomotive force AH is necessary.
It should be noted, however, that to go from state
equally spaced from both narrow walls, with the long di 25 (1) to state (3) requires a ?nite time. The mere ap
plication of a reverse magnetomotive force will not,
mension of vane 31 extending longitudinally along the
instantaneously, reverse the ?ux within the gyromagnetic
guide, parallel to the guide walls.
material. Since it is necessary for the purposes of the
Vane 31 is biased by a steady magnetic ?eld at right
invention to change the magnetization in a time that is
angles to the direction of propagation of the wave energy
short
compared to the spin wave build-up time, the am
30
in guide 30. As illustrated in FIG. 3, this ?eld may be
plitude of the reversing force must be adjusted accord
supplied by an electrical solenoid having a magnetic core
ingly. Speci?cally, if the spin wave build-up time is
32 and pole pieces N and S bearing upon. the wide walls
Tw, the switching time 'rs should be greater than Tw. The
of guide 30- in a region substantially coextensive with the
magnetomotive force Hm required to switch at this rate
gyromagnetic vane 31. Turns of wire 33 are wound
about core 32 and connected through a potentiometer 34 35 is then
posed within guide 30 along the longitudinal guide axis
to a source of magnetizing current 35.
The operation of the phase shifter shown in FIG. 3
is based upon the effective permeability presented to the
propagating wave. Since resonant absorption represents
where SW, the switching coe?icient, and H0, the threshold
a loss for these applications, these devices operate in a 40 ?eld, are constant of the material and are determined
experimentally. A typical value of SW is 0.2 oe.;isec.,
range of applied magnetic ?elds between zero and that re
while H0 is approximately equal to 2H6. The spin wave
quired to initiate the resonant phenomenon. In particu
build-up time, Tw, being a function of the material, its
lar, the region of magnetic saturation is of primary im
geometry and the radio frequency power level, is also
portance since the effective permeability is greatest in this
region. At power levels below the critical power level, 45 determined experimentally. This can be done by sud
denly applying a radio frequency wave greater than the
low-loss phase shift is readily obtained. However, above
critical power level to the gyromagnetic element biased
the critical power level coupling between the imiform
below resonance. Momentarily the output will rise to
magnetic precession and the spin waves gives rise to the
full transmission. As power is coupled to the spin
above-described subsidiary resonance effect which, for all
practical purposes, substantially destroys the usefulness 50 waves and the spin waves build up, the output will ex
ponentially fall off until a lower steady state output is
of the phase shifter.
reached. The time for the output to decline to approxi
In accordance with the invention the tendency to cou
mately 37 percent of the peak output is one time con
ple energy to the spin waves is inhibited by changing the
stant, or 'rw. In a preferred embodiment ¢S is made
direction of magnetization within the gyromagnetic vane
31. In the embodiment of the invention shown in FIG. 55 equal to Tw/ 10.
In the embodiment of the invention shown in FIG. 3,
3 this is done by modulating the steady biasing ?eld by
given for the purpose of illustration, it is assumed that
means of a high frequency signal having an amplitude
the gyromagnetic material is transversely biased to satu
and frequency which will be explained in greater detail
ration and that the function of the microwave device is
hereinafter. The modulating ?eld is impressed upon the
magnetic ‘core 32 by turns of wire 37 which connect to a 60 to introduce phase shift. It is to be understood, however,
that for the purposes of this invention the function of
high frequency energy source 36.
the device could just as well be to introduce attenuation
For simplicity, source 36 is shown in FIG. 3 as a sepa
into the microwave system and for that purpose the gyro
rate generator. It is understood, however, that source 36
magnetic material is biased to gyromagnetic resonance.
would generally be associated with 1a power level detec
tor that would monitor the power level in guide 311 and 65 As was explained hereinbefore, when a resonantly biased
attenuation is operated above the critical power level,
only gate source 36 on when the power level in guide 30
the overall attenuation tends to decrease. By modulat
exceeded the critical power level of the gyromagnetic
ing the steady biasing ?eld, as explained hereinbefore,
medium.
coupling between the uniform precession and the spin
In operation, potentiometer 34 is adjusted to produce a
steady biasing ?eld having an amplitude su?iciently large 70 Waves is impeded and the tendency for the attenuation
to decrease is avoided.
to produce saturation in vane 31. So biased, the mag
It will also be noted that in the illustrative embodi
netization throughout the material is aligned parallel to
ment of ‘FIG. 3 the modulating ?eld completely re
the direction of the biasing ?eld. Wave energy, having
verses the direction of the biasing ?eld. However, as
an amplitude less than the critic-a1 amplitude for the gyro
magnetic material, will propagate along guide 3%? and 75 was pointed out, it is only necessary to change the direc
3,051,917
7
e
tion of the magnetization within the gyromagnetic ma
terial. This would also include a change in direction
less than 180 degrees. A modi?cation of the embodiJ
ment of FIG. 3 wherein changes in the direction of
magnetization less than 180 degrees are utilized as shown
in FIG. 5.
a pencil of gyromagnetic material disposed along the lon
gitudinal axis of a rectangular section of waveguide. In
this type of phase shifter the gyrornagnetic element is
longitudinally biased below saturation. While modula—
tion of the longitudinal magnetic ?eld in accordance with
the principles of the invention will extend the power han
The device shown in FIG. 5 comprises a section of
waveguide 50, and a vane of gyromagnetic material 51
taneous phase shift produced by the device will also vary,
disposed therein.
thus introducing'what could ‘be an objectionable phase
Vane 51 is biased by a steady mag
dling capabilities of this type of phase shifter, the instan
netic ?eld Hdc at right angles to the direction of propa~ 10 shift ripple in the output wave.
gation of the wave energy in guide 50. This ?eld may
This di?iculty, however, may be readily obviated by
be supplied by an electric solenoid, by a permanent mag
modifying the phase shifter as shown in FIG. 6. Speci?
netic structure, or vane ‘51 may be permanently mag
cally, the overall phase shift is obtained in two parts by
netized if desired.
dividing the gyromagnetic element into two portions and
In the embodiment of FIG. 5 the steady biasing ?eld 15 separately controlling the magnetic ?elds applied to each
Hdc is modulated by means of locally generated mag
of the two portions. The phase shifter shown in FIG. 6
netic ?elds which tend to alter the direction of the bias
comprises ‘a section of rectangular waveguide 60 within
ing ?eld. These local ?elds are produced by means of
which there are suitably supported two ‘cylindrical rods
a conductive member 52 which is threaded through the
61 and 62 of gyromagnetic material. Rods 61 and 62 are
gyromagnetic vane 51. As shown in FIG. 5, conductor 20 longitudinally disposed within guide 60 along the guide
52 lies in a plane perpendicular to the electric ?eld in
axis and are longitudinally biased by means of solenoids
guide 50 and passes through the broad surface of vane
63 and 64, respectively, mounted outside of waveguide 60.
51 over a region coextensive with the longitudinal di
Solenoid 63 is connected through potentiometer 65 to a
mension of the vane. Conductor 52 is energized by
source of magnetizing current 66. Similarly, solenoid 64
means of the high frequency energy source 53.
25 is connected through potentiometer 67 to said source of
As before, when the amplitude of the wave energy
magnetizing current 66.
is less than the critical level, source 53 is off. As the
Since the rods are biased below saturation, the direction
power level of the propagating wave increases and ap
of magnetization is not parallel to the biasing ?eld but
proaches the critical level, source 53 is gated on, ener
instead varies throughout the volume of the rods. Thus,
gizing conductor 52 and producing local magnetic ?elds 30 the instantaneous direction of magnetization can be varied
about conductor 52 in the region of the gyromagnetic
by merely varying the intensity of the biasing ?eld. Ac
element. Speci?cally, the magnetic ?eld produced by
cordingly, the modulating ?eld is applied parallel to the
the modulating source 5-3 comprises closed loops 54
biasing ?eld by means of the two additional solenoids 68
surrounding conductor 52. The effect of these ?eld com
and 69, each of which extends over a region of guide 60
ponents is to alter the direction of the net magnetic 35 substantially coextensive with one of the rods. Solenoids
?eld over most of the volume of the gyromagnetic vane,
68 and 69 are energized from the same high frequency
thereby minimizing the tendency for energy to couple
energy source 70. However, inserted in the circuit asso
between the uniform precession and the spin waves. The
amplitude of the modulating ?eld will depend upon the
application; that is, if the device shown in FIG. 5 is a
ciated with solenoid 69 is the phase shifter 71 for intro:
ducing a 180 degree phase difference between the modu
lating current in solenoid 69 and the modulating current
in solenoid 68, as will be explained in greater detail here
inafter.
‘Curve 80 of FIG. 7 shows the phase shift produced by
each of the gyromagnetic rods, in the embodiment shown
phase shifter, the amplitude of the modulating ?eld is
adjusted so as to maintain the attenuation through the
device below a speci?ed maximum for the given oper
ating level. If, on the other hand, the device in FIG. 5
is intended to be a resonant attenuator, then the ampli
tude of the biasing ?eld is adjusted so as to maintain
the attenuation above a speci?ed minimum at the de
in FIG. 6, as a function of the instantaneous magnetizing
?eld H. Assuming a total desired phase shift of 183 de
grees, the magnetizing ?eld produced by solenoid 63 is
adjusted to H1, producing a phase shift ,81 along rod 61,
ing rate is related to the spin wave build-up time for the
and the magnetizing ?eld produced by solenoid 64 is ad
given gyromagnetic element.
50 justed to H2, producing a phase shift ,82 along rod 62,
It is apparent from the above discussion that the net
Where Bl+B2:B3
e?ective magnetization within the gyromagnetic element
> As the amplitude of the wave energy propagating along
sired operating level. As before, however, the modulat
is varied as a function of time. While the desired effect
guide 60 approaches the critical level, source 70 is ener
of this variation is to disrupt the coupling between the
gized subjecting rods 61 and 62 to a varying magnetic
magnetization and the spin waves, it also tends to modu 55 ?eld component which modulates the phase shift pro
late the instantaneous phase shift or attenuation produced
duced by each of said rods. Let us consider rod 61 ?rst.‘
by the microwave device. If the resulting overall phase
Under the in?uence of solenoid 68, the total magnetiz
shifter the resulting overall attenuation is still su?icient
ing ?eld within rod 61 will start to increase, causing the
for the purpose intended, this modulation, or ripple, pro
total phase shift produced by rod 61 to increase in ac
duced by the modulating wave may be tolerable. If, how 60 cordance with the variation de?ned by curve 80. Let
ever, the variations produced 'by the modulating wave are
us assume that the total magnetizing ?eld for rod 61 in
not permissible, corrective measures can be taken. Per
creases to a point H1’. The total phase shift produced by
haps the simplest corrective measure consists in cascading
rod 61 is then increased to [31’. ‘Because of the 180 de
a number of gyromagnetic elements and suitably phasing
gree phase shift produced ‘by phase shifter 71, the effect
the modulating ?eld impressed upon them so as to re 65 of the modulating ?eld produced by solenoid 69 is to re
duce the net modulating ripple to a speci?ed minimum
duce the total magnetizing ?eld in rod 62 from Hz to H2’,
level. A simple embodiment of such an arrangement is
causing the total phase shift in this section of the device
shown in the structure of FIG. 6, which is basically a
to decrease ‘from ,82 to ,6'2'. Because curve 80 is substan
phase shifter of the type described by F. Reggia and E6.
tially linear in the region under consideration, B1’+;82' is
Spencer in ‘an article entitled “A New Technique in ‘Fer 70. substantially equal to til-H32. Thus, the total phase shift
rite Phase Shifting for Beam Scanning of Microwave An- .
through the two sections of the phase shifter remains sub
tennas,” November 1957, Proceedings of the I.R.E., pages
stantially constant even though the individual phase shift
1514-4517, modi?ed in accordance with the principles of
in each section may vary instantaneously due to the effect
the invention.
'
of the modulating ?eld. It is obvious that by suitably
The tic-called Reggia-Spencer phase shifter comprises 75 arranging the phasing of the modulating ?elds, the num
3,051,917
her of gyromagnetic rods may be increased and the total
1%
for reversing the direction of said biasing ?eld at a
phase shift divided among these additional rods, further
reducing any ripple in the overall phase shift.
rate l/TS greater than the reciprocal of the spin wave
build-up time for said material, said reversing ?eld having
In all cases it is understood that the above-described
arrangements are illustrative of a small number of the
an amplitude
many possible speci?c embodiments which can represent
applications of the principles of the invention. Numerous
where H0 is the threshold ?eld for said material, and
‘SW is the switching coefficient.
accordance with these principles by those skilled in the
6. The combination according to claim 5 wherein the
‘art without departing from the spirit and scope of the 10
switching
rate l/¢s is approximately equal to 10‘/Tw
invention.
7. A phase shifter for electromagnetic wave energ
What is claimed is:
comprising a section of conductively bounded waveguide
1. An electromagnetic wave transmission device com
supportive of said wave energy, ?rst and second elongated
prising a section of guided wave path having an element
elements of ferromagnetic material disposed in longi
15
of ferromagnetic material disposed therein, said material
tudinal succession within said waveguide, each of said
characterized as having a ?rst transmission constant for
and varied other arrangements can readily be devised in
applied signals below a critical power level and a second
transmission constant different than said ?rst constant
for applied signals above said critical power level, said
elements presenting a ?rst propagation constant to wave
energy below a given power level and a second propaga
tion constant to wave energy above said given power level,
each ‘of said elements also having a given spin wave build
material further characterized as having a given spin wave
up time, means for longitudinally magnetizing said ?rst
build-up time, means for establishing a given state of
element at a ?rst ?eld intensity, means for longitudinally
magnetization within said material, means for applying
magnetizing
said second element at a second ?eld intensity
electromagnetic wave energy to said section of wave path
greater than said ?rst intensity, where said ?rst and sec
having a power level greater than said critical power
ond intensities are less than that necessary to produce
level, and means for preventing said material from assum
saturation in said elements, means for applying electro
ing said second transmission constant including means for
magnetic wave energy to said waveguide having a power
modulating said given state of magnetization at a rate not
level greater than said given power level, and means
less than the reciprocal of the spin wave build-up time of
for increasing said ?rst ?eld intensity an incremental
said material.
2. The combination according to claim 1 wherein the 30 amount AH, and means for decreasing said second ?eld
intensity an incremental amount substantially equal to
direction of magnetization within said material is reversed
AH at a rate greater than the reciprocal of said given spin
by said modulating means.
wave build-up time for said elements with the variation
‘3. The combination according to claim 1 wherein the
in said ?rst element being 180 degrees out of time phase
direction of magnetization within said material is caused
with respect to the variation in said second element.
to change ‘by said modulating means by an amount less
8. A device for electromagnetic wave energy compris
than 180 degrees.
ing
a section of conductively bounded waveguide sup
4. A high power, low-loss, microwave device includ
portive of said wave energy, a plurality of n elements of
ing an electromagnetic wave transmission path having a
power saturable ferromagnetic medium disposed therein,
ferromagnetic material disposed in longitudinal succes
said medium characterized as having a low positive atten 40 sion within said Waveguide, each of said elements present
ing a ?rst propagation constant to wave energy below a
uation constant for applied signals below a critical power
given power level and a second propagation constant to
level, but capable of exhibiting a high positive attenuation
wave energy above said given power level, each of said
constant to signals above said critical power level, said
elements also having a given spin wave build-up time,
medium further characterized as having a given spin
Wave build~up time, means for applying a steady magnetic . means for magnetically biasing each of said elements at
a di?erent ?eld intensity, means for applying electro
biasing ?eld to said medium, means for applying electro
magnetic wave energy to said waveguide having a power
magnetic wave energy to said path having a power level
level greater than said given power level, and means for
greater than said critical power level, and means for pre
varying said different ?eld intensities at a rate greater
venting said medium from exhibiting said high attenuation
constant including means for modulating said magnetic 50 than the reciprocal of said given spin wave buid-up time
for said elements with the variation in each of said ele
?eld at a rate not less than the reciprocal of the spin wave
ments differing in phase by an amount equal to 360/ n
build-up time of said medium.
degree or whole multiples thereof.
5. A microwave phase shifter comprising a guided elec
tromagnetic wave transmission path having an element
References Cited in the ?le of this patent
of ferromagnetic material disposed therein, said medium 55
UNITED STATES PATENTS
characterized as having a low positive attenuation for
applied signals below a critical power level but capable
2,798,205
Hogan ________________ __ July 2, 1957
of exhibiting a high positive attenuation to signals above
2,820,200
Du Pre ______________ __ Jan. 14, 1958
said critical power level, said medium further character
2,847,647
Zaleski ______________ __ Aug. 12, 1958
ized as having a given spin wave build-up time 'rw, means 60
for applying a steady magnetic biasing ?eld Hdc to said
medium in a given direction, means for applying electro
magnetic wave energy to said wave path having a power
level greater than said critical power level, and means
OTHER REFERENCES
Wheeler: “IRE Transactions on Microwave Theory
and Techniques,” January 1958, pages 38-39.
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